Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Title: Optical Tool Assembly For Improved RCW And Lens Edge
Formation
Inventors: Thomas G. Jones
Bruce E. Lawton
RELATED APPLICATION
This application is related to U.S. patent applications entitled "NON-
OPTICAL MULTI-PIECE CORE ASSEMBLY FOR RAPID TOOL CHANGE" (U.S.
Serial No. 11/026,620, filed December 30, 2004), "CORE LOCKING ASSEMBLY
AND METHOD FOR ORIENTATION OF ASYMMETRICAL TOOLING" (U.S. Serial
No. 11/027,381, filed December 30, 2004) and "OPTICAL TOOL ASSEMBLY"
(U.S. Serial No. 11/027,380, filed December 30, 2004); all filed concurrently
herewith, commonly assigned to Bausch & Lomb Incorporated and expressly
incorporated herein by reference.
BACKGROUND
The present disclosure relates to the molding of articles of manufacture.
More particularly, the disclosure relates to an improved optical tool assembly
for
injection molding mold sections or preforms having an improved right cylinder
wall
(RCW) which are used in the manufacture of ophthalmic lenses, including
contact
lenses and intraocular lenses, having an improved lens edge formation and will
be
described with particular reference thereto. It is to be appreciated, however,
that
the improved optical tool assembly and apparatus related thereto is adaptable
for
effective use in other environments and applications.
One method in practice for making ophthalmic lenses, including contact
lenses and intraocular lenses, is cast molding. Cast molding of ophthalmic
lenses
involves depositing a curable mixture of polymerizable lens materials, such as
monomers, in a mold cavity formed by two assembled mold sections, curing the
mixture, disassembling the mold sections and removing the molded lens. Other
post-molding processing steps, for example, hydration in the case of hydrogel
lenses, may also be employed. Representative cast molding methods are
disclosed in U.S. Pat. Nos. 5,271,875 (Appleton et al.); 4,197,266 (Clark et
al.);
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4,208,364 (Shepherd); 4,865,779 (Ihn et al.); 4,955,580 (Seden et al.);
5,466,147
(Appleton et al.); and 5,143,660 (Hamilton et al.).
When cast molding between a pair of mold sections, typically one mold
section, referred to as the anterior mold section or preform, forms the
anterior
convex, optical surface of the ophthalmic lens and the other mold section,
referred
to as the posterior mold section or preform, forms the posterior concave,
optical
surface of the ophthalmic lens. The anterior and posterior mold sections are
generally complimentary in configuration. They are joined together during the
molding process to form a lens forming or molding cavity. Once the lens is
formed,
the mold sections or preforms are separated and the molded lens is removed.
The
anterior and posterior mold sections are usually used only once for casting a
lens
prior to being discarded due to the significant degradation of the optical
surfaces of
the mold sections that often occurs during a single casting operation.
Formation of the mold sections used in casting a lens occurs through a
separate molding process prior to cast molding of the lens. In this regard,
the mold
sections are first formed by injection molding a resin in the cavity of an
injection
molding apparatus. More particularly, mounted in the injection molding
apparatus
are tools for forming the mold sections. Typically, the tools are fitted into
mold
plates in the injection molding machine and the mold sections are produced by
injection molding a selected resin between opposed sets of injection molding
tools.
The tools are typically made from brass, stainless steel, nickel, or some
combination thereof and, unlike the mold sections which are used only once,
are
used again and again to make large quantities of mold sections.
The injection molding tools are typically formed in accordance with the
specification of the corresponding ophthalmic lens surfaces to be formed on or
by
the mold sections. That is, the ophthalmic lens being produced determines the
specific design of the mold sections. The needed mold section parameters, in
turn,
determine the design of the corresponding injection molding tools. The
injection
molding tools are typically manufactured to extremely high specifications
and/or
tolerances so that no roughness or surface defects are transferred to the mold
sections being made from the tools. Any such defects on the mold sections,
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particularly on an optical surface of a mold section, is likely to be
transferred to, and
appear on, the finished lens during the cast molding operation.
Each mold section, whether it be a posterior mold section or an anterior
mold section, includes an optical surface (posterior optical surface on a
posterior
mold section and anterior optical surface on an anterior mold section) that
forms a
surface of the ophthalmic lens, as well as a non-optical surface. When
injection
molding the mold section, the injection molding apparatus typically includes
an
optical tool assembly having an optical molding surface for forming the
optical
surface of the mold section and a non-optical tool assembly for forming the
non-
optical surface of the mold section, which is opposite the optical surface. As
is
known to those skilled in the art, the optical molding surface can be changed
for
purposes of producing mold sections of different thicknesses, which are in
turn
used to produce ophthalmic lenses of varying powers.
Often, the -anterior mold section includes a right cylinder wall (RCW)
adjacent a periphery of its optical surface. The RCW of the anterior mold
section is
used to form the final edge of the ophthalmic lens produced by the mold
section
and is desirably controlled to tight tolerances. Heretofore, the RCW was
formed by
an optical tool insert being selectively positioned within a body. The optical
tool
insert included a primary molding surface for forming the optical surface of
the mold
section and a secondary, cylindrical mold surface for forming the RCW.
Typically,
shims were used to position the optical insert relative to the body until
sufficient
protrusion of the cylindrical molding surface was reached for forming the RCW.
The use of shims cause tool setup difficulties, including the need for
numerous iterative attempts to achieve the desired protrusion of the optical
tool
relative to the body, which requires additional downtime of the injection
molding
machine in which the tool assembly is employed. Moreover, gaps often result
between the tool insert and the body which manifests as plastic flash near the
RCW
when cast molding the lens. This ultimately leads to potentially fatal defects
being
contained within the ophthalmic lens. Any improvements to the optical tool
assembly that would eliminate the need for shims and/or eliminate (or at least
reduce) the occurrence of gaps which ultimately create flash are considered
desirable, particularly those that reduce injection molding machine downtime.
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BRIEF SUMMARY
According to one aspect, an optical tool assembly is provided for use in an
injection molding apparatus opposite a non-optical tool assembly to form an
ophthalmic mold section. More particularly, in accordance with this aspect,
the
optical tool assembly includes a cavity ring mounted to an associated mold
plate
and an optical insert removably secured to the cavity ring. The optical insert
has an
optical molding surface thereon for forming an optical surface of the
ophthalmic
mold section. The optical molding surface has a right cylindrical wall (RCW)
molding portion for forming a RCW of the ophthalmic mold section. The RCW
molding portion is formed adjacent a peripheral edge of the optical insert.
According to another aspect, an apparatus for injection molding an
ophthalmic lens mold is provided and has an optical surface and a non-optical
surface opposite the optical surface. More particularly, in accordance with
this
aspect, the apparatus includes a non-optical tool assembly for forming a non-
optical
surface of the ophthalmic lens mold and an optical tool assembly in opposed
relation to the non-optical tool assembly that together therewith forms a mold
cavity
for forming the ophthalmic lens mold. The optical tool assembly includes a
cavity
ring and an optical tool insert. The cavity ring is removably secured to a
mold plate
of an injection molding apparatus. The optical tool insert has an optical
molding
surface thereon for forming the optical surface of the ophthalmic lens mold.
The
optical tool insert is removably secured to the cavity ring. A right
cylindrical wall
(RCW) molding portion of the optical molding surface is formed adjacent a
peripheral edge of the optical molding surface. The RCW molding portion forms
a
T-shape with a cavity ring molding surface.
In accordance with yet another aspect, an injection molding apparatus is
provided for forming a mold section which is subsequently used for forming an
ophthalmic lens. More particularly, in accordance with this aspect, the
injection
molding apparatus includes a mold member mounted to an associated first mold
plate. An optical tool insert is removably mounted to the mold member. The
optical
tool insert has a molding surface with an optical quality finish that includes
a right
cylindrical wall (RCW) forming a peripheral edge of the optical tool insert. A
core
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member is mounted to an associated second mold plate opposite the associated
first mold plate. A non-optical tool insert is removably mounted to the core
member.
The non-optical insert has a non-optical molding surface for forming a surface
of
the mold section opposite the optical surface.
In accordance with still yet another aspect, a method for forming an
ophthalmic lens is provided. More particularly, in accordance with this
aspect, an
apparatus is provided for injection molding an ophthalmic lens mold section
having
an optical surface and a non-optical surface opposite the optical surface. The
apparatus has a non-optical tool assembly for forming the non-optical surface
of the
ophthalmic lens mold section and an optical tool assembly in opposed relation
to
the non-optical tool assembly that together therewith forms a mold cavity for
forming the ophthalmic lens mold section. The optical tool assembly includes a
cavity ring removably secured to a mold plate of an injection molding
apparatus and
an optical tool insert having an optical molding surface thereon for forming
the
optical surface of the ophthalmic lens mold section. The optical tool insert
is
removably secured to the cavity ring. A right cylindrical wall (RCW) molding
portion
of the optical molding surface is formed adjacent a peripheral edge of the
optical
molding surface. The RCW molding portion forms a T-shape with a cavity ring
molding surface. The ophthalmic lens mold section is injection molded in the
mold
cavity. The ophthalmic lens mold section is removed from the cavity. The
ophthalmic lens mold section is matched to a mating ophthalmic lens mold
section.
An ophthalmic lens is cast molded between the ophthalmic lens mold section.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGURE 1 is a schematic exploded view of a representative mold section
assembly forming an ophthalmic lens.
FIGURE 2 is a schematic cross-sectional view of the mold section assembly
of FIGURE 1 showing mating mold sections in nesting relation.
FIGURE 2a is an enlarged, partial, schematic cross-sectional view of the
mold sections of FIGURE 2.
FIGURE 3 is a schematic cross-sectional view of an injection molding
arrangement having tool assemblies (including an optical tool assembly and a
non-
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optical tool assembly) for injection molding an anterior mold section of the
mold
assembly shown in FIGURES 1 and 2.
FIGURE 4 is an enlarged partial view of the optical tool assembly of FIGURE
3.
FIGURE 5 is a rear perspective view of an optical tool insert of the optical
tool assembly of FIGURE 4.
FIGURE 6 is a front perspective view of the optical tool insert of the optical
tool assembly of FIGURE 4.
FIGURE 7 is a side elevational view of the optical tool insert of the optical
tool assembly of FIGURE 4.
FIGURE 7a is an enlarged partial elevational view of the optical tool insert
of
FIGURE 7.
DETAILED DESCRIPTION
Referring now to the drawings wherein the showings are for purposes of
illustrating one or more embodiments and not for purposes of limiting the
same, a
representative mold assembly is shown in FIGURE 1 and generally designated by
reference numeral 10. The mold assembly 10 includes an anterior mold preform
or
section 12 and a posterior mold preform or section 14. When the mold sections
12
and 14 are assembled, optical surfaces 16,18 of the mold sections 12,14 define
a
mold cavity in which an ophthalmic lens 20 is formed, such as by cast molding.
The
ophthalmic lens 20 can be, for example, a contact lens or intraocular lens.
The
optical surface 16, also referred to herein as an anterior molding surface, is
a
concave surface that forms a convex, anterior side 22 of the lens 20 and the
optical
surface 18, also referred to herein as a posterior molding surface, is a
convex
surface formed opposite non-optical surface 24 that forms a concave, posterior
side
26 of the lens 20. In the illustrated mold assembly 10, with additional
reference to
FIGURE 2, mold sections 12,14 additionally include respective cylindrical
walls
28,30 and segment walls 32,34 that nest (but not necessarily touch or contact
one
another) when the mold sections are fully assembled.
As will be described in more detail below, each of the mold sections 12,14,
also referred to herein as ophthalmic lens molds, can be injection molded from
a
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plastic resin, such as polypropylene, polyvinyl chloride (PVC) or polystyrene,
for
example, in a full injection molding apparatus. As will be understood by those
skilled in the art, the injection molded sections 12,14 can then be used
together as
shown in FIGURE 2 in a cast molding process wherein a curable lens material,
such as a liquid polymerizable monomer mixture, is introduced onto the
anterior
molding surface 16, mold sections 12,14 are brought into close association
with the
liquid being compressed to fill lens mold cavity 36 formed between the mold
sections 12,14, and the monomer mixture is cured into an ophthalmic lens, such
as
contact lens 20 shown in the illustrated embodiment. It should be readily
appreciated by those skilled in the art that modified mold sections could be
formed
and applied in the above-described cast molding process to produce any type of
lenses, such as, for example, spherical, toric, multifocal lenses and
intraocular
lenses.
As will be understood by those skilled in the art, tool assemblies are
mounted in the injection molding apparatus for forming the mold sections 12,14
by
injection molding. The tool assemblies are mounted to and/orfitted into mold
plates
of the injection molding apparatus and the mold sections 12,14 are formed by
injection molding a selected resin in a cavity formed between opposed sets of
tool
assemblies. With additional reference to FIGURE 3, only tool assemblies for
forming the anterior mold section 12 will be described in further detail
herein.
In FIGURE 3, mold section mold cavity 40 is formed between opposed tool
assemblies, including optical tool assembly 42 and non-optical tool assembly
44, in
which the mold section 12 can be formed. As illustrated, the optical tool
assembly
42 forms the optical surface 16 of the mold section 12 and the non-optical
tool
assembly 44 forms non-optical surface 46 (FIGURE 2) on an opposite side of the
surface 16. The tool assemblies 42,44 also combine to form the cylindrical
wall 28
and the segment wall 32.
With reference to FIGURE 2a, the anterior mold section 12 includes a right
cylinder wall (RCW) 48 formed at a periphery of the optical surface 16
adjacent the
segment wall 32. In the cast molding process, the RCW 48 forms a final edge 50
(FIGURE 1) of the lens 20. More specifically, the RCW forms a slight taper
along
the lens edge 50 which enhances the comfort of the lens 20 for a wearer
thereof.
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Without the RCW, the lens edge 50 would have a significantly larger edge
profile
which could lead to discomfort for the wearer. In the illustrated embodiment,
the
posterior mold section 14 includes a tapered surface 52 between optical
surface 18
and segment wall 34 which combines with the RCW48 of the anterior mold section
12 to form lens edge 50 as a beveled edge. The beveled edge 50 reduces sharp
angles at the periphery of the lens 20 allowing the lens to better float in a
user's eye
and help keep the eye free of undesirable deposit build-up.
The optical tool assembly 42 includes a mold member, which in the
illustrated embodiment is cavity ring 56, and an optical tool insert 58
mounted to the
cavity ring. The optical tool insert 58 is removably secured to the cavity
ring 56 by a
suitable fastener, such as a threaded member or cap screw 60. With further
reference to FIGURE 4, the optical tool insert 58 includes optical molding
surface
62 which has an optical quality finish to form the anterior molding optical
surface 16.
As used herein, the term "optical quality finish" denotes a molding surface
that is
sufficiently smooth for forming optical surface 16 which ultimately forms the
anterior
side 22 of the ophthalmic lens 20. By having a optical quality finish, the
lens 20
produced by the anterior molding surface 62 is suitable for placement in one's
eye
without the need to machine or polish the formed lens surface 22.
As will be appreciated by those skilled in the art, the insert 58 can be one
of
a set or series of inserts (not shown) and the removeability of the insert 58
enables
it to be readily changed with another insert from the set of inserts. Each of
the
inserts in the set can have a different optical molding surface for purposes
of
ultimately molding lenses having differing optical powers. The cavity ring 56
is
removably secured to a mold plate 64 of the injection molding apparatus.
Fasteners, such as threaded members or cap screws 66, are used to releaseably
secure the cavity ring 56 to the mold plate 64 and to maintain the position of
the
cavity ring during injection molding of the mold section 12.
With continued reference to FIGURES 3 and 4, the optical tool insert 58 is
received in a recess 68 defined in a front surface 70 of the cavity ring 56
and a
shaft portion 58a of the insert 58 is received within another recess 72
defined in a
central protuberance 74 extending from a rear side 76 of the cavity ring.
Recess 68
also forms a cavity ring molding surface that forms a portion of the mold
section 12.
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In the illustrated embodiment, this portion is an outer surface of the
cylindrical wall
28 and the segment wall 32 of the mold section 12. As already indicated, the
screw
60 removably secures the insert 58 to the cavity ring 56. A head portion 58b
of the
insert 58 protrudes into the recess 68 and includes the optical molding
surface 62
that forms the optical surface 16 of the mold section. More specifically, the
screw
60 is received in a throughhole 80 defined centrally through the protuberance
74
and threadedly engaged to the insert 58 in a threaded bore 81 defined in the
shaft
portion 58a. A head 60a of the screw 60 is received in counterbore 85.
A molding dowel 82 extends into the mold cavity 40 from dowel bore 84
defined in the cavity ring 56. The molding dowel 82 marks the mold section 12
with
an indent (not shown) in the segment wall 32 to record the rotational
orientation of
the mold section 12 in the mold cavity 40. With additional reference to
FIGURES 5
and 6, the shaft portion 58a includes a radially extending portion 58c which
is
spaced from the head portion 58b. An axially extending recess 86 is defined in
the
portion 58c which receives a dowel member 88 extending radially from the
cavity
ring 56 into the recess 72. Cooperation between the dowel 88 and the recess 86
rotatably aligns the insert 58 relative to the cavity ring 56 to orient any
non-
rotationally symmetrical feature on insert 58 in a prescribed orientation
relative to
the remaining mold parts.
With still additional reference to FIGURES 7 and 7a, the insert 58 includes
an RCW molding surface 90 formed adjacent a peripheral edge 92 of the molding
surface 62 of the insert 58. The RCW portion 90, also referred to herein as an
RCW molding surface, forms the RCW48 in mold section 12 shown in FIGURE 2a.
The RCW molding surface 90 extends axially relative to the insert 58 and is
generally parallel to a mold cavity axis 122. A curved junction portion 94
connects
or transitions the RCW portion 90 to the rest of the molding surface 62. The
RCW
portion 90 and the junction portion 94 allow the insert 58 to be installed in
the cavity
ring 56 without the use of shims, thus enabling the insert 58 to be installed
in a
single setup step (i.e., no iterative setup steps are required for setting up
the.RCW
molding surface). The RCW molding portion 90 terminates into the cavity ring
molding surface 70. The RCW molding portion 90 is oriented approximately
normal
relative to the cavity ring molding surface 70, which flanks the RCW surface
90 and
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no gap is formed between the RCW molding portion 90 and surface 70 so flash is
reduced or eliminated. The RCW molding portion 90 forms a T-shape with the
cavity ring molding surface 70.
Though the illustrated embodiment shows the optical insert 58 directly
secured to the cavity ring 56, it is to be appreciated that other alternate
arrangements are possible and are to be considered within the scope of the
present
invention. For example, the cavity ring can be formed of two parts: an outer
cavity
ring and an inner body member. In this arrangement, the insert 58 is secured
by
the fastener 60 to the body member and the body member is slidably received in
a
central opening of the cavity. Such an arrangement could enable faster insert
changes. More details of such an arrangement are provided in commonly
assigned, copending U.S. patent application entitled "Optical Tool Assembly,"
filed
concurrently herewith and expressly incorporated herein by reference.
As illustrated, with specific reference back to FIGURE 3, the cavity ring 56
mates with the non-optical tool assembly 44 along a parting line 100 to form
the
closed mold cavity 40. In one embodiment, the non-optical tool assembly 44
includes a core member 102, a non-optical insert or cap 104 and a stripper
member
106 (which can be a stripper plate or sleeve, for example) annularly received
about
the core member. The non-optical insert 104 includes a first molding surface
108
that forms the surface 46 opposite the optical surface 16 of the molding
section 12
and a second molding surface 110 that forms an inner surface of the
cylindrical wall
28 and an inner surface of the segment wall 32. The non-optical insert 104 is
removably secured to the core member 102 which can be conventionally secured
to
the injection molding apparatus. Of course, as would be apparent to one
skilled in
the art, the exact design or configuration to accommodate the molding assembly
44, as well as the molding assembly 42, will depend on the injection molding
apparatus.
In one embodiment the insert 58 and the cavity ring 56 of the optical tool
assembly 42 are formed of brass, stainless steel, nickel, or some combination
thereof. The molding surfaces 62,68, can be formed according to methods
generally known to those skilled in the art, such as, for example, lathe
cutting or
electrodischarge machining. The optical molding surface 62 (including RCW and
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junction molding portions 90,94) can additionally be polished to achieve
precision
surface quality so that no, or only insignificant, surface imperfections are
transferred
to the mold section 12. On the non-optical tool assembly 44, the core member
102
can be formed of a highly thermal conductive material such as beryllium copper
(BeCu), while the insert 104 can be formed of a material that is more
desirable to
machine from an environmental/biohazards standpoint, such as copper, nickel or
tin
alloys. The molding surfaces 108,110 can be formed according to generally
known
methods such as lathe cutting or electrodischarge machining. The non-optical
insert molding surface 108, used to form the non-optical surface 46 opposite
the
optical surface 16, does not require an optical quality finish as it does not
contact
the polymerizable lens mixture in the lens casting process. Thus, the surface
108
does not require the same degree of polishing as the optical molding surface
62
which is used to form the optical surface 16. However, some polishing or
grinding
may still be required.
A runner or sprue 114 is disposed between the tooling assemblies 42,44 and
fluidly connects to the cavity 40 for allowing molten resin to be injected
into the
cavity 40 when injection molding the mold section 12. In the illustrated
embodiment, the runner 114 connects to the cavity 40 along a portion thereof
that
forms the cylindrical wall 28 and thereby does not interfere with the molding
of the
optical surface 16. The runner 114 is formed by a first channel 116 defined in
the
cavity ring 56 and a second channel 118 defined in a stripper member 106,
which is
aligned with the first channel 116.
A parting line interface 120 between the insert 58 and the cavity ring 56
(more particularly, between the molding surface 62 and the first surface 70)
is
oriented along a plane that is approximately normal or perpendicular relative
to
draw experienced in the molding process. In particular, the interface 120 is
formed
between head 58b of insert 58 and surface 70 of the cavity ring 56. The
interface
120 is oriented approximately normal relative to mold cavity axis 122. In the
illustrated mold cavity 40, the direction of the draw will be substantially
parallel to
mold cavity axis 122. As a result, the portion of the mold section 12 formed
by the
RCW molding surface 90 can be formed completely free, or with at least
significantly less, flash. In the event that flash is formed between the
insert head
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portion 58b and the cavity ring 56, when the tool assemblies 42,44 are
separated,
the flash should likewise become separated from the molded mold section 12.
Positioning the RCW molding surface 90 adjacent the peripheral edge 92 of
the insert 58 has the additional advantage of improving the squareness (as
opposed to the previously observed occasional rounding) molded on the mold
section 12 adjacent the RCW 48. This has the effect of producing a more
uniform
and repeatable mold section 12, particularly the portion of which that is
molded by
the RCW surface 90 which translates directly into a lens edge 50 of improved
quality. Thus, the insert 58 with the RCW surface 90 adjacent the periphery
edge
92 has the effect of reducing the cost of manufacturing by reducing setup
time, as
well as improving the final part quality of the molded lens 20.
The exemplary embodiment has been described with reference to one or
more embodiments. Obviously, modifications and alterations will occur to
others
upon reading and understanding the preceding detailed description. It is
intended
that the exemplary embodiment be construed as including all such modifications
and alterations insofar as they come within the scope of the appended claims
or the
equivalents thereof.
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